\section{High Temperature Hardening}
\label{sec:temperature}
For ITER, the possible operating conditions are summarized in the Table
\ref{tab:temperature}.

\begin{table} [htbp]
\centering
\caption{Possible temperatures at inspection environment in ITER
\cite{ITEROrg.2004}.}
	\label{tab:temperature}
	\begin{tabular}{l l}
		\bfseries Description & \bfseries First Wall Temp. \\
		\hline
		Scheduled Inspection & 120\textcelsius \\
		Inspection at baking temperature & 240\textcelsius \\
		Unscheduled Inspection & 120\textcelsius \\
		Maintenance & 50\textcelsius \\
	\end{tabular}
\end{table}

Considering the temperature constraint, all the materials properties,
particularly tensile strength and elastic modulus, must be considered at
120\textcelsius\ but the material must also perform at baking temperature
(240\textcelsius). For instance, most aluminum alloys are forbidden for
structural purposes, because their mechanical properties are not suitable at
these temperatures. The Articulated Inspection Arm (AIA) \cite{Keller2009} and
tokamak diagnostic \cite{Smick2005} experiences tell that lubrication could be a
serious issue as well.

\subsection{Temperature Distribution}
If the different parts of the robot are at different temperatures a problem may
occur due to thermal dilatation, which may result in gaps or additional stress
in the mechanism.

A solution to avoid this problem is to design the entire robot to
uniformly reach 120\textcelsius. In this case, the outer parts of the robot
should act like black bodies, radiating in order to heat up the whole robot
at 120\textcelsius.

Therefore materials may also be chosen with dilatation constants near each
other. For materials with different dilatation constant extra care is required
during the robot design phase, since all parts will be fabricated at room
temperature (20\textcelsius\ approx.). This may also be a problem if testing has
to be done at room temperature.
\subsection{Temperature Insulation}
Despite the efforts that can be made to find high temperature compliant
components, there are some components that must not be exposed to
high-temperature environment. In this case the solution is to confine these
components in a cage made of reflective material and since the robots will be in
an ultra-high vacuum environment the main heat transfer mode will be radiation
and a reflective cage would take a lot of time to get the nominal temperature.

Considering the temperature of the vacuum vessel, most of the energy
exchange is through infrared radiation. Therefore a good design will imply that
the components inside the cage could be working for a long period of time.

The robots joints must be designed taking into account the thermal
insulation in order to minimize the conduction heat transfer. This solution is
exactly the opposite of the temperature distribution strategy. In case these two
solutions must be used for different components, it is recommended to
provide a very accurate model for each of them. 

Clearly this is a real difficulty since thermal repartition gets as complex as
the assembly design. If some parts may not reach the outgassing temperature long
enough, extra care against it must be taken. Other possible solution is to
design a cooler system with a cold fluid or gas and to use a heat exchanger
outside the bio-shield.